<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Document</title>
  </head>
  <body>
    <script>
      fun();	// 报错，提示fun is not a function（fun不是一个函数）
      var fun = function () {
        console.log('fn');
      };
    </script>
  </body>
</html>